Far more people TRIED to clear than actually cleared. The work, practice, memorization, team meetings, and social networking that goes into every actual clear went a very long way towards keeping the game active. A good chunk of people will at least try to learn the rotations, stat weights, melds, and food that goes into successful clears even if they aren't actually planning to run it themselves and that keeps the game active.
It's like the 200 PotD run. There were far, far more failed clears then people who got to take a picture on the bench at the bottom. Every attempt, every grind to get your weapon and armor maxed, people coming up with tactics for getting past chimeras, keeps the game active.
Sometimes the horse never gets the carrot on the stick before it goes bad or loses interest, but the walk leading to that point would have been much shorter without it.